Photonic crystals are periodic dielectric structures having band gaps that inhibit the propagation of a certain frequency range of electromagnetic radiation (e.g., visible light, infrared, microwave, etc.). Photonic crystals include regularly repeating internal regions of high and low dielectric constant. Whether electromagnetic radiation (i.e., streams of photons) propagates through a photonic crystal depends on the radiation's wavelength as well as various properties of the crystal.
Two-dimensional (2D) photonic crystal slabs confine light by Bragg reflection in-plane and total internal reflection in the third dimension. Introduction of point and line defects into 2D photonic crystal slabs create localized resonant cavities and PhC waveguides respectively. Such defect cavities in high-index contrast materials possess strong confinement with subwavelength modal volumes (Vm) at approximately (λ/n)3, corresponding to high field intensities per photon for increased nonlinear interaction. Moreover, photonic crystal cavities with high quality factors (Q) have been achieved recently, now permitting nanosecond photon lifetimes for enhanced light-matter interactions. The strong localization and long photon lifetimes in these high-Q/Vm photonic crystal nanocavities point to enhanced nonlinear optical physics such as optical bistability, Raman lasing, and cavity quantum electrodynamics in silicon photonics. However, these applications can require precise control of resonant wavelength emissions to achieve desired device performance.